High density integrated circuit (IC) packages that house Large Scale Integration/Very Large Scale Integration type semiconductor devices are well known. Input/output pins for such IC packages are often arranged in such a dense pattern (sometimes more than two hundred closely spaced contacts) that direct soldering of the IC package to a substrate; such as a printed wiring or circuit board (PCB) creates several significant problems related to inspection and correction of any resulting soldering faults.
Land grid array (LGA) connectors are known for interconnecting IC packages to PCB's. LGA's typically do not require soldering procedures during engagement with the PCB. Prior art LGA assemblies are also known which include an insulative housing and a plurality of resilient electrical contacts received in passageways formed in the housing. The resilient electrical contacts typically have exposed portions at the upper and lower surfaces of the insulative housing for engaging contact pads. When an IC package is accurately positioned in overlying aligned engagement with the conductive input/output contacts of a typical IC package, a normal force is applied to the exposed portions of each resilient electrical contact to electrically and mechanically engage the respective contact pads.
The resilient electrical contacts associated with prior art LGA's have had a variety of shapes and electrical properties. A commonly used form of resilient electrical contact includes two free ends connected by a curved portion which provides for the storage of elastic energy during engagement with the IC package and PCB. Prior art resilient electrical contacts are usually a single metal structure in the form of a spring to provide the required elastic response during service while also serving as a conductive element for electrical connection. They often also include a metallic shield for enhanced electrical properties. Typically, a combination of barrier metal and noble metal platings are applied to the surface of the spring for corrosion prevention and for electrical contact enhancement. It is often the case that these platings are not of sufficient thickness for electrical conduction along the surface of the spring.
Examples of such prior art resilient conductive contacts may be found in U.S. Pat. Nos.: 6,477,058; 6,471,524; 6,464,511; 6,439,897; 6,439,894; 6,416,330; 6,375,473: 6,338,629; 6,313,523; 6,302,702: 6,299,460; 6,299,457; 6,264,476; 6,224,392; 6,183,269; 6,183,267; 6,174,174; 6,174,172; 6,079,987; 6,074,219; 6,042,388; 6,033,233; 6,032,356; 5,967,798; 5,919,050; 5,806,181; 5,791,914; 5,772,451; 5,727,954; 5,718,040; 5,663,654; 5,540,593; 5,519,201; 5,473,510; 5,462,440; 5,428,191; 5,388,998; 5,388,997; 5,366,380; 5,362,241; 5,334,029; 5,299,939; 5,273,438; 5,248,262; 5,237,743; 5,232,372; 5,214,563; 5,213,513; 5,211,566; 5,207,585; 5,192,213; 5,184,962; 5,174,763;5,167,512; RE34,084; 5,139,427; 5,061,191; 5,035,628; 5,030,109; 5,007,842; 4,961,709; 4,922,376; 4,838,815; 4,820,376; 4,810,213; 4,707,657; 4,620,761; 4,508,405; 4,203,203; 4,029,375; 3,934,959; 3,795,884; 3,513,434; 3,317,885; 2,153,177, which patents are hereby incorporated herein by reference.
A problem in the art exists in that a good material for the construction of a spring, such as a high strength steel, is not a very good electrical conductor. On the other hand, a good electrical conductor, such as a copper alloy or precious metal, is often not a good spring material. In addition, the need for sufficient contact forces to be provided by the spring very often dictates its shape and size. The optimization of these parameters very often results in less than optimal electrical performance.
In particular, the characteristic impedance of the electrical contact is often moved toward undesirable levels as a result of the physical design of the spring, necessitating the use of a shielding material. It is desirable to have a controlled characteristic impedance of the signal from the IC to the printed circuit board without discontinuity, since the close proximity of the electrical contacts often results in cross-talk at a higher data rates. This cross-talk problem may also be alleviated by connecting alternate contacts to ground so as to provide an electrical reference, but at the expense of achievable interconnection density. It is therefore desirable to provide a connector assembly between the IC and a PCB which has a controlled impedance, exhibits wave guide properties with low electrical resistance, provides a short electrical length with high density, and is reliable.
There is a need for a more simplified resilient conductive contact which incorporates the seemingly opposing requirements of good spring properties, high conductivity, and enhanced signal transmission performance. Therefore, an improved electrical contact for use in an LGA socket or electrical connector is needed which can overcome the drawbacks of conventional electrical contacts.